This invention relates to systems for correcting deflection from a normal path of movement of a belt trained over a plurality of rollers, and more particularly it is concerned with a belt deflection correcting system of the type described which is suitable for use with a belt conveyor device using a conveyor belt or a copying apparatus using a photosensitive belt.
Various type of systems have hitherto been available for correcting deflection of a belt from its normal path of movement. In all these systems, the belt is forcedly returned to the left or the right depending on the direction of deflection thereof. For moving the belt in the desired direction, a belt supporting roller is usually tilted with respect to its center axis. Japanese Utility Model Application Laid-Open No. Sho-56-20405 discloses a system for correcting deflection of a belt from its normal path of movement by tilting the center axis of a roller. In the system disclosed, a sensing plate is arranged along either side edge of the belt in a position in which the sensing plate is brought into contact with the respective side edge of the belt, and the sensing plates are connected together by a connecting rod, so that when the belt is deflected from its normal path of movement in one direction, the side edge of the belt is brought into contact with the sensing plate located on the side toward which the belt is deflected. As further deflection of the belt causes the sensing plate and the connecting rod to move, a switch located in a suitable position is actuated to render operative a hydraulic cylinder connected to one end of the support shaft of the roller. The hydraulic cylinder causes the center axis of the roller to tilt, to thereby move the belt in a direction opposite the direction of its deflection to allow it to move along its normal path of movement.
Some disadvantages are associated with this system. Since the belt is brought at its side edges into contact with the sensing plates, the side edges of the belt might suffer damage. Also, when the side edges of the belt are not straight, the movement of the sensing plates coming into contact with the side edges of the belt would be unstable, so that misoperation of the hydraulic cylinder might result. When the belt undergoes vibration, misoperation of the hydraulic cylinder might occur.
In case that the switch is actuated by the movement of the sensing plate, the switch would not essentially be actuated unless the deflection of the belt exceeds a predetermined amount. Thus tilting of the shaft of the roller in response to a deflection of the belt would be delayed, making it impossible to correct a belt deflection occurring in a small amount.